In a liquid pump, in order to prevent a liquid from intruding into a motor casing from the side of a pump casing through a rotating shaft, a bearing portion of the rotating shaft is provided with a sealing mechanism for disposing a mechanical seal or a packing.
In a sealing mechanism located at the circumference of the rotating shaft, the sealing members are always in contact with the rotating shaft irrespective of the operating state or non-operating state of an electric motor and, therefore, easily wear down and impose a heavy maintenance burden.
In addition, in a liquid pump, depending on the usage place and application, not only the liquid but also minute solids may intrude into the circumference of the rotating shaft. Consequently, in the prior mechanism for sealing at the circumference of the rotating shaft, sealing members are easily damaged.
In view of the above circumstances, sealing mechanisms utilizing electromagnets have been proposed and carried out. For example, Japanese Patent Publication No. H01-43159 teaches a construction wherein a ring seal is fixed in a brim shape to a rotating shaft and a ring seal is attached to a cylindrical supporting body disposed in a manner shift-able in the axial direction of the rotating shaft. Both are opposed to each other The cylindrical supporting body is operated by an electromagnet. When an electric motor is in operation, by turning on the effect of the electromagnet, the cylindrical supporting body is shifted to closely fit both ring seals to create a sealing state, and when an electric motor is not in operation, by turning off the effect of the electromagnet, the cylindrical supporting body is restored by a spring or the like to release close fitting between both ring seals.
On the other hand, Japanese Patent Publications No. S62-46717 and Japanese Patent Publication No. S62-49477 teaches a construction wherein joining and separation of opposed ring seals are controlled by centrifugal force produced by a rotation of a rotating shaft when an electric motor is in operation.
In addition to the above, a construction for sealing by utilizing centrifugal force produced by a rotation of a rotating shaft is disclosed in Japanese Unexamined Patent Publication No. H07-280105, etc. However, this is carried out by only mechanical structures and is different from the construction of the present invention.
Since, the sealing mechanism taught in the above-described Japanese Patent Publication No. H01-43159 has a construction wherein joining and separation of the opposed ring seals are carried out by turning on and off of the electromagnet, technical problems remain, including: (1) a power supply circuit for operating the electromagnet is required, which results in a high cost, moreover, (2) since power supply voltages are not uniform among countries and regions, an adjustment is required prior to utilization; (3) the space where the electromagnet is arranged requires water-tightness, which complicates the mechanism; and (4) since temperature of the watertight space rises due to heat generated by the electromagnet and condensation easily condenses in a stop state, there is a concern for malfunction.
On the other hand, Japanese Patent Publications No. S62-46717 and No. S62-49477, as described above, concerns a sealing mechanism in that joining and separation of the opposed ring seals are controlled by centrifugal force produced by a rotation of the rotating shaft when an electric motor is in operation. However, since all components are mechanically structured, technical problems remain, including: (1) accurate processing and assembling of members or operating adjustments are required; and, (2) a malfunction easily occurs when minute solid components, etc., intrude, and the maintenance burden is great.
In particular, in a prior sealing mechanism, an O-ring or an oil seal is required in a sliding portion for driving a sealing member up and down. However, in some cases, expansion, corrosion and the like due to chemicals exist in the sliding portion, and the sealing member cannot smoothly follow the movement of the rotating shaft due to frictional resistance. Consequently, the prior liquid pump has a problem of an increased maintenance burden.